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Last edited Sun Dec 29, 2024, 10:52 PM - Edit history (1)

Spectator video shows something happened to the right engine on approach, possibly a bird strike or a compressor stall following an earlier bird strike. At this point, flaps appear to be deployed but the landing gear is up.
A FlightRadar24 statement says no ADS-B data (altitude, speed, heading, etc.) was received after the bird strike, potentially indicating an electrical failure or damage to the transmitter.

There are unconfirmed reports of fume in the cockpit.
737NG oxygen masks normally mix oxygen with ambient air but an "emergency" mode can be used to supply 100% oxygen under positive pressure.
The cockpit windows can also be opened safely during flight, at least at low speed.

Despite media reports of bad weather, METARs in fact report nearly perfect flying conditions: winds were almost calm, visibility was good, there were a few clouds at 4,900 ft., no precipitation in the area, and temperatures were slightly above freezing.

Preliminary information indicates that after the bird strike, the aircraft flew for about 9 minutes as it circled back to the airport from the opposite direction (from the north) and attempted to land. This indicates it was controllable and had at least partial engine power. The flight path as currently understood is not consistent with a complete engine failure scenario as experienced in US Airways 1549 (the Hudson landing).

From the deeply distressing footage of the landing, the leading-edge and trailing-edge flaps appear to be fully retracted. This "clean wing" configuration would have required a very high approach speed, likely close to 200 knots, versus 140-150 knots for a typical landing.
Some video viewers see heat blur and/or hear engine power from at least one engine during the landing. Personally, I can't distinguish potential heat blur from compression artifacts in the video and from dust/smoke generated by contact with the ground. Similarly, it's hard to distinguish potential engine sound from aerodynamic noise and friction with the ground, so my own view is that the videos are not conclusive.

The 737NG has two independent main hydraulic systems: system A is powered by the left engine and system B is powered by the right engine. Aircraft services are divided between the two systems. An additional standby hydraulic system is driven by an electric motor and operates a small number of critical services, including the rudder, leading-edge flaps, and thrust reversers. If both engine-driven electrical generators are inoperative, electricity is provided by the auxiliary power unit (if running) or by a standby battery that provides about 30 minutes of electricity. Some 737s are equipped with two batteries providing 60 minutes of backup power, which is apparently an EASA requirement; the accident aircraft was initially delivered to Ryanair, so it may have had two.

Primary flight controls (ailerons, elevators, rudder) are actuated by both main hydraulic systems.
Leading-edge flaps/slats are directly actuated by system B and by the standby system. Additionally, in the event of a loss of pressure to system B, a power transfer unit automatically uses system A to pressurize system B for leading-edge flap/slat deployment.
Trailing-edge flaps are actuated by system B.
Landing gear is actuated by system A.

Flight crews train intensively for failure of an engine and the associated hydraulic system in every phase of flight (this is probably the single most trained scenario) and crews should be deeply familiar with how the aircraft behaves in this situation. In an actual emergency, the crew would immediately complete a small number of memory items and then refer to the appropriate checklist in the quick reference handbook for additional steps to troubleshoot and/or mitigate the issue.

On the 737, the nose gear doors are held closed by system A. In the event of a loss of hydraulic pressure, they will open under their own weight. Notably, the doors appear to be closed as the aircraft landed, which implies that system A was functioning. (The 737 does not have main gear doors; when the gear is retracted, the wheel rims sit flush with the fuselage and the struts are covered by attached panels.)
The above notwithstanding, in the event of complete loss of hydraulic pressure:
Ailerons and elevators are actuated via cable relays from the control columns, albeit with a significantly higher force requirement than typical.

Landing gear can be manually released via a set of handles located under an access cover on the cockpit floor next to the first officer. When the handles are pulled, the gear will deploy under its own weight.
Flaps can be deployed by backup systems via a switch located on the overhead panel. Trailing-edge flap deployment using the alternate electrical system is significantly slower than a hydraulic deployment
.
A landing gear warning horn will sound if any landing gear is not down and locked in the following conditions:
Flaps 0°-10°, thrust levers below 20° (or 34° with one engine inoperative), altitude below 800 ft radar altimeter (cannot be silenced below 200 feet)
Flaps 15°-25°, thrust levers below 20° (or 34° OEI) (cannot be silenced)
Flaps 30°-40°, regardless of altitude and thrust lever position (cannot be silenced)

The aircraft appears to have touched down about halfway down the runway and was still traveling at very high speed (calculated upthread as approximately 130 knots) when it departed the end of the runway.
A second video suggests the pilot "floated" the landing for a gentle touchdown and then may have maintained nose-up elevator to mitigate loads on the engines. This suggests the flight crew was aware they were making a gear-up landing and that gear deployment was not simply overlooked. However, holding the aircraft's weight off the engines would have reduced friction with the ground and thus deceleration.

There is no indication that spoilers deployed on touchdown. When 737NG auto spoilers are armed, deployment is triggered by either weight on the right main landing gear or by any two of the three landing gear wheels spinning up to more than 60 knots. Thus, spoilers would not automatically deploy in a gear-up landing scenario. Speed brakes (flight spoilers) can be manually commanded at any time via the cockpit spoiler handle.
Inboard and outboard flight/ground spoilers on each wing are powered by different hydraulic systems.
Ground-only spoilers on both wings are powered by system B.

Although a dark band appears around the right engine immediately after touchdown that is visually similar to thrust reverser deployment, Jon Ostrower believe this represents damage to the engine cowling upon contact with the ground, creating only the appearance of reverser deployment. There is no visual indication that the left reverser deployed.
On the 737NG, reverser deployment requires the thrust levers to be moved to the reverse position, as well as either a weight sensor in the right landing gear determining the aircraft is on the ground or the radio altimeter detecting below 10 feet to the ground. Thrust reversers are actuated by system A on the left engine and by system B on the right engine. Both reversers are also actuated by the standby system.

About 450 feet beyond the end of the runway, the aircraft struck a berm supporting the localizer antenna array and was completely destroyed on impact. The localizer is part of the instrument landing system that provides guidance to aircraft on approach and it must be positioned on the centerline near the runway threshold. Presumably the localizer was elevated to provide a better signal, but elevated terrain so close to a runway is not recommended; the International Civil Aviation Organization standard requires a 90 m / 300 ft runway end safety area and recommends an additional 240 m / 790 ft beyond that. At LAX, for example, one localizer is mounted on a metal frame that would be secured to the ground with breakaway connections to limit damage to an aircraft in a collision.
Many localizers are mounted directly on the ground, again with breakaway bolts. However, given the aircraft's extremely high speed when it departed the runway, it is speculation to assert what might have happened had the berm not been present.